The invention relates to a device for setting the angular position of optical elements applicable to advantage for optical measurements, e.g. for setting the angular position of mirrors and lenses around a specific axis with interferometric and unvarying accuracy.
It is common knowledge that in the course of realizing the optical measuring arrangements, all optical elements of the arrangement have to be set in relation to the beam path. The required setting accuracy is determined by the optical measurement to be realized. As the laser becomes generally used in the practice, the setting accuracy is to be interferometric, i.e. identical with or more accurate than the wavelength of the light. This means that the angular position of the optical elements requires setting accuracy within a few seconds and resetting accuracy less than one second.
In the known devices used for setting the angular position of optical elements, the structural members moving in relation to each other are interconnected with slipping or rolling elements. It is generally known that in case of such devices improvement of the setting accuracy is restricted by the stick slip resulting from the slipping or rolling friction of the structural members moving in relation to each other. The resetting accuracy generally well exceeds the value of 10 seconds (e.g. in case of the Hungarian patent application No. MA 2835), where the value of angle resolution is 30 seconds.
In the Hungarian patent specification No. 177 299, an angle-setting device is described, provided with torsional bearing formed by plate springs.
This angle-setting device provides the optical path for the beam of light with a through hole in the axis of rotation. Since the kinematic contact between the object table and the stationary part of the device is free from external friction, the stick slip is therefore eliminated. This however involves the use of such deformation joint instead of the kinematically well defined link work, the kinematic functioning of which depends not only on geometric but other parameters (e.g. strength, assembly) and on the load as well. Consequently, the fact that the position of the axis of rotation of the torsional bearing built up with plate springs is considerably influenced by two factors, i.e. deviation of the spring constants of the plate springs and the load determined by the mass of the optical element to be set, represents a serious drawback.
The spring constants of plate springs are determined by several parameters, e.g. geometry, composition, heat treatment, etc., hence even in case of the most careful production technology, a considerable deviation of the spring constant has to be reckoned with.
Further shortcoming of the device is that uniformity of the clamping on both ends of the plate springs cannot be ensured even with the most careful assembly. Another shortcoming is the relatively large external dimension pertaining to the internal through hole, as well as its extremely careful and therefore costly production technology.
The final result of the described shortcomings is that the device is suitable only for such kinds of setting purpose, where drifting of the axis of rotation of the optical element is permissible. Consequently, the above described device is not suitable for the unvarying setting of optical elements with interferometric accuracy, hence it is unobtainable in the trade.